The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Inverters employ power switches, e.g., insulated gate-drive bipolar transistors (IGBTs) or MOSFETs to convert high-voltage DC electrical power to high-voltage AC power that is transferred to an electric motor/generator to generate torque for tractive effort in vehicles employing hybrid-drive and electric-drive powertrain systems. Faults in such systems include line-to-line electric shorts, ground faults, and shoot-through conditions in the power switches of the inverter, the electric motor/generator, and a multi-phase power bus electrically connected between the inverter and the electric motor/generator. Faults associated with power switches and windings of the electric motor/generator may result in excess electric current flow through the various components, and an increased voltage magnitude across a collector and emitter of one or more of the power switches, referred to as desaturation. One known fault mode is a shoot-through condition, wherein upper and lower switches in the same inverter leg are switched ON at the same time. This condition causes a shoot-through condition wherein the DC bus is shorted. This condition produces a voltage dip on the DC bus.
Known power switches are controlled to one of an ON condition and an OFF condition. When in the ON condition with the power switch functioning as designed, electric current through the power switch is saturated, i.e., all available current passes through the switch with a small portion dissipating into heat energy due to switch resistance. When in the OFF condition, the switch blocks flow of electric current.
A desaturation fault in a power switch can cause electric current to increase beyond a maximum operating limit, wherein the power switch enters a linear mode, thus desaturating the power switch (DSAT). A DSAT condition is said to exist when the voltage magnitude across a collector and emitter (Vce) of a power switch rises above a threshold, e.g., 1-2 volts when a gate-emitter voltage is high. Known control system responses to a DSAT fault include an immediate shutdown of the electric motor/generator. Known systems are configured to monitor power switch collector-emitter voltages to detect DSAT faults, and include control systems to effect an immediate shutdown of the electric motor/generator upon detection of a DSAT fault. Powertrain systems are exposed to external disturbances including electromagnetic interference (EMI) that may trigger false detection of a fault and an associated immediate shutdown of the electric motor/generator that is unnecessary.
Known DSAT diagnostic methods involve employing a hardware circuit to monitor electric parameters and executing remedial action designed to protect hardware and systems from electrical or heat damage. One known method of monitoring to protect against DSAT faults includes measuring a voltage drop between a collector and an emitter on each power switch. Known hardware-based DSAT diagnostics are designed to respond quickly to a perceived fault, but require circuitry that must be designed and implemented during system development when system properties are not all known. Therefore hardware-based diagnostics can suffer from false-positive fault triggers due to hardware circuitry production tolerance variations and unexpected system events. Due to hardware imperfections and tolerance stack-up issues, hardware-based DSAT diagnostics may produce a false-positive DSAT signal leading to unnecessary shutdown of the electric motor/generator. A known method of compensating for issues associated with hardware-based DSAT diagnostics includes employing diagnostic software that includes a retry routine wherein a first hardware diagnostic trip does not trigger a system wide shutdown. Known retry routines clear or erase faults detected by the hardware-based diagnostics and allow the system to restart a calibratable number of times using a retry counter. The quantity of retries for the hardware-based diagnostic can be a predetermined fixed value. This fixed quantity of retries creates a protection from nuisance trips, but can create an overstress condition for hardware when a real fault is present.